HF RL Explorer

Fix PayPal purchase-unit field names and add shipping-discount breakdown support

Fix PayPal purchase-unit field names and add shipping-discount breakdown support: a task in bird-critic-1.5-full-300 (Harbor dataset). The PayPal Orders v2 API requires the field invoice id , but the plugin currently emits invoice number in two places:

The task

The PayPal Orders v2 API requires the field `invoice_id`, but the plugin currently emits `invoice_number` in two places:

Part of kochsnow/bird-critic-1.5-full-300.